The disposal of solid waste materials has become a problem for public and private organizations. Recycling programs have successfully used only a portion of this waste stream, however. A good portion of the waste stream is either burned or introduced into landfills.
Through the years, the amount of solid waste generated by individual households, businesses, and governmental units has increased. Disposal of such waste materials has become more difficult. The inconvenience of waste disposal has increased along with the environmental impact of the solid waste on land use, potable water, the atmosphere, and the natural environment.
Recycling efforts have had some success; however, a good portion of recyclable materials is not recycled and remains as solid waste. In order to obtain valuable materials, solid waste materials have been treated or pretreated. None of these pretreatment processes has been widely accepted in view of the relatively high cost and low efficiency. Attempts to introduce apparatus, systems, and processes for treating waste material to form a useful fuel and a recyclable stream is found in Anderson U.S. Pat. Nos. 5,445,329; 5,540,391; 5,655,718; and PCT WO 95/13148, and also in Garrison et al. PCT WO 00/72987. These references disclose apparatus, methods, and processing of municipal solid waste (MSW) into fuel and recyclable streams such as glass, metal, and plastics.
These prior art processes involve an apparatus that can be used to treat solid waste material. The waste material is placed into a vessel, contacted with steam, and processed at increased temperature and pressure. The variety in moisture, temperature, and pressure within the vessel contacting the solid waste under conditions of rotary agitation can cause the solid waste product to break down into a useful burnable solid fuel and can also result in formation of easily separable metal, glass, and plastic streams that can be readily removed from the solid fuel material using conventional separation techniques based on magnets, density, and particle size-type separating systems such as a trommel or flat bed separator.
The vessel in these prior art systems that is used to treat the solid waste requires the application of pressure to successfully treat the solid waste efficiently. The pressure, up to 600 psig (about 4200 kPa), about 60 psig (about 410 kPa) or as little as 10 psig (about 100 kPA), can be maintained within the vessel between charging and discharging the vessel using a closure system. The prior art apparatus and processes, while adequately treating the solid waste for the purpose of obtaining fuel and separable streams, have their productivity reduced by the difficulty in attaching the closure after charging and then removing the closure from the vessel for the purpose of discharging the treated waste. To address this situation, the assignee has described in co-pending PCT Publication WO 2006/041439 and WO 2006/041437 (both incorporated herein by reference) a pressure vessel closure system for use with a pressure vessel that is easily opened and closed during operation at the appropriate operating pressures.
The prior art Anderson U.S. Pat. Nos. 5,445,329; 5,540,391; 5,655,718; and related PCT WO 95/13148 each describe using multiple vessel systems. These prior art disclosures describe transferring steam between the vessels in order to have an efficient system. However, it has been found that the twin vessel system proposed in these Anderson patents can be improved with respect to efficiency due to issues with steam transfers and also due to timing constraints put on the system. Improvements are desirable.